Transcript Physico-chemical Parameters of the Okavango Delta Water

ENVIRONMENTAL CHEMISTRY
APCH 211
Dr. J. Catherine Ngila
SCHOOL OF PURE AND APPLIED CHEMISTRY
UNIVERSITY OF KWAZULU-NATAL, WESTVILLE CAMPUS,
DURBAN
Chemistry H-BLOCK Room 357 Ext 3103
JC Ngila, UKZN, Chemistry Westville
Durban. [email protected]
1
OVERVIEW OF TOPICS TO BE COVERED

Introduction

What is Environmental chemistry? Definitions
 Atmospheric Chemistry
 What is the typical composition of atmosphere above earth?
 Toxicity of materials
 What substances are considered toxic?
 Natural Waters:
 what is normally found?
 Water treatment for domestic consumption
 What process is involved?
 Sewage treatment
 What process is involved?
 Industrial effluent management
 How to manage discharged effluent?
 Solid waste management
 How to manage solid as compared to liquid waste?
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2
Recommended textbook?

A list of textbooks has been given in the course
outline.

The main book is:
Gary W. vanLoon and Stephen J. Duffy
Environmental Chemistry: A global perspective, 2nd Edn,
Oxford University Press, 2005.
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Introduction
What is Environmental chemistry? Definitions
Definition

Environmental chemistry is the scientific
study of the chemical and biochemical
phenomena that occur in natural places. It
includes aquatic chemistry and soil
chemistry.
Environmental chemistry can be defined as
the study of the sources, reactions, transport,
effects, and fates of chemical species in the air,
water and soil environments; and the effect of
human activity on these.
Reference
http://en.wikipedia.org/wiki/Environmental_chemistry
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Continued….Defn of Enviro Chem

Environmental chemistry is an interdisciplinary science
that includes atmospheric, aquatic and soil chemistry, and
heavily relies on analytical chemistry and is related to
environmental science.

Environmental Chemistry offer the following:


Help understand how the uncontaminated
environment works, which chemicals, and what
concentrations are present naturally and their
effects?
Baseline levels- necessary so as to accurately
study the effects humans have on the environment
through the release of chemicals.
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Definition 2: Enviro Chem

Environmental chemistry is essentially the
science of identifying and measuring the
amount of chemicals species in the
environment, natural or manmade.

It also includes the study of the fate and effects
of these chemicals species in the environment.
Reference: http://www.ela-iet.com/el00004.htm
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Concepts of Environmental Chem

Environmental chemists draw on a range of concepts
from chemistry and various environmental sciences to
assist in their study of what is happening to a
chemical species in the environment.

Important general concepts from chemistry include
understanding chemical reactions and equations,
solutions, units, sampling, and analytical techniques
[1].
Reference
[1] Williams, Ian. Environmental Chemistry, A Modular Approach. Wiley.
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2001.
7
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Contid…. Concepts of Enviro Chem
Various environmental concepts include the
following:
(i) Contamination and (ii) environmental Indicators
i) A Contaminant is a substance present in nature due to human
activity, that would not otherwise be there
The term contaminant is often used interchangeably with pollutant,
which is a substance that has a detrimental impact on the
environment it is in.
Whilst a contaminant is sometimes defined as a substance present in
the environment as a result of human activity, but without harmful
effects, it is sometimes the case that toxic or harmful effects from
contamination only become apparent at a later date.
The medium (e.g. soil) or organism (e.g. fish) affected by the pollutant
or contaminant is called a receptor, whilst a sink is a chemical
medium or species that that retains and interacts with the pollutant
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Environmental indicators






Chemical indicators of water quality
include:
pH
Conductivity
Dissolved Oxygen (DO)
Chemical oxygen demand (COD)
Biological (biochemical) oxygen demand
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Perspectives of Atmosphere



The atmosphere to be discussed in this
module is that of the Earth.
However, the atmosphere of each planet is
unique.
The atmosphere of the other planets is
mostly hydrogen and helium.
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The Earth’s atmosphere:


Atmosphere is a thin shell of gases surrounding
the earth. The major components of the
atmosphere near the surface of the Earth are:
 Nitrogen = 78.08%
 Oxygen = 20.95%
 Argon = 0.93%
 Carbon dioxide = 0.0378%
 Moisture = ranging 0.5 -3.5%
Note that the %concentrations are based on dry
atmosphere.
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Atmospheric Chemistry…......
Definitions of atmospheric chemistry :


The study of the composition of and chemical
transformations occurring in the atmosphere.
Studies in atmospheric chemistry include:




Field measurements,
Computer modeling, and
Laboratory measurements,
They all requires an understanding of the interaction of
the atmosphere with the biosphere and anthropogenic
influences in order to be able to explain current
conditions and to predict future changes.
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Atmospheric chemistry
Atmospheric chemistry is a multidisciplinary field of
research in which the chemistry of the atmosphere is
studied.

It involves physics, meteorology, computer
modeling, oceanography, geology and volcanology and
other disciplines.

Reference
en.wikipedia.org/wiki/Atmospheric_chemistry
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Atmospheric Chemistry
What is the Earth’s Atmosphere?
 Atmosphere is protective blanket above the Earth
and protect it from hostile environment of outer
space
 The atmosphere provides carbon dioxide for plants;
oxygen for respiration and nitrogen required for
nitrogen cycle and for ammonia manufacturing
industry.
 Atmosphere is the source of many molecules:
 Nitrogen-containing molecules like proteins
 Carbohydrates
 Fats & oils
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[email protected]
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Contid…….Atmosphere here xxx!!
Atmosphere as dumping ground?

In the negative sense, the atmosphere has been
used as the dumping ground for many pollutants.
Examples
i.
It absorbs most of the cosmic rays from outer
space and protects organisms from their effects.
ii.
It absorbs most of the electromagnetic radiation
from the sun and allows selected radiation in the
regions of 300 -2500nm, such as near-UV (300400nm), visible (400-800nm), and near-IR (9002500nm) and radio waves in the region 1x 107 to
40x 109nm.

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Regions of the Atmosphere


The atmosphere can conveniently be divided
into mainly four (or five) sections based on
whether temperature decreases or increases
with altitude.
Temperature fluctuations are caused by
thermodynamic changes which is a measure
of kinetic energy of molecules in the
atmosphere.
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Altitude above (distance above sea level)

From low to high altitude, the classes are:
i.
Troposphere = 0-15 km, Temp decrease with
altitude
ii.
Stratosphere = 15-50 km, Temp increase with
altitude
iii.
Mesosphere = 50-85 km, Temp decrease with
altitude
iv.
Thermosphere =85-500 km, Temp increase
with altitude
v.
Exosphere = 500-520nm, No much change in
Temp
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Atmosphere Classes

Troposphere
- A region of intense convective mixing. Contains
approximately 85% by mass of the entire
atmosphere.
-Tropopause is the upper boundary of
troposphere which marks the altitude at which
the direction of temperature change reverses.
-The troposphere is marked by strong convective
over-turnings, whereby large parcels of warm air
travel upwards to the tropopause, carrying water
vapor and forming clouds as they cool down.
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…. …Troposphere

Troposphere is in contact with the Earth’s
surface and therefore interacts directly with
other climate subsystems, such as the
biosphere (the land and vegetation), the
hydrosphere (the oceans), the cryosphere (the
ice caps), the lithosphere (the topography), and
most all, with the human world (Peixoto and
Oort, 1992).
Reference: J.P. Peixoto and A.H. Oort, "Chapter 2: Nature of the
Problem", Physics of Climate, AIP, 8-26, 1992.
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Stratosphere
In this region, temperature increases with
altitude upto approximately -2º C at 50km.

The
upper boundary is called stratopause at
which convective mixing is relatively stable.
Rates for loss of O3 exceed rates for production by
about 40 percent at 40 km
The rapid loss of O3 beginning in the mid-1970s at
low altitudes over Antarctica in the spring is due
primarily to catalytic cycles involving halogen
radicals.
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Contid…. Atmosphere Classes
Mesosphere
Temperature decreases with increasing altitude
to -90ºC at 85km. The upper boundary is
called mesopause.


The chemical substances are in an excited
state, as they absorb energy from the Sun.
The regions of the stratosphere and the
mesosphere, along with the stratopause and
mesopause, are called the middle
atmosphere.
Thermosphere
This region stretches from 85500km.Temperature increases upto
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Durban.
[email protected]
1200ºC
at 500KM
Thermosphere
This region stretches from 85500km.Temperature increases upto
1200ºC at 500KM
The regions of the stratosphere and the
mesosphere, along with the stratopause and
mesopause, are called the middle
atmosphere.
Exosphere= 500-520nm at ~1200 ºC
The region above 700 km, at which height
atoms may begin to escape into space is
known as the exosphere.
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Atmospheric Compostion
Atmospheric composition
Average composition of dry atmosphere by volume (Gasper, NASA)
Nitrogen, N2 78.084%
Oxygen, O2
20.946%
Argon, Ar
0.934%
Water Vapour, H2O
Highly variable; 01-5% (typically 1-3%)
Concentrations
Carbon
350 ppmv
Neon
18.18
Helium
5.24
Methane
1.7
Krypton
1.14
Hydrogen
0.55
Notes: the concentration of CO2 and CH4 vary by season and location.
*ppmv represents parts per million by volume.
The mean molecular mass of air is 28.97 g/mol.
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History of Atmospheric chemistry



The ancient Greeks regarded air as one of the four
elements, but the first scientific studies of atmospheric
composition began in the 18th century.
Chemists such as Joseph Priestley, Antoine Lavoisier
and Henry Cavendish made the first measurements of
the composition of the atmosphere.
In the late 19th and early 20th centuries interest shifted
towards trace constituents with very small
concentrations. One particularly important discovery for
atmospheric chemistry was the discovery of ozone by
Christian Friedrich Schoenbein in 1840.
Reference: http://en.wikipedia.org/wiki/Atmospheric_chemistry
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Contid…..Atmosp Chem…20th Century

In the 20th century atmospheric science moved on
from studying the composition of air to a
consideration of how the concentrations of trace
gases in the atmosphere have changed over time
and the chemical processes which create and
destroy compounds in the air.

Two particularly important examples of this were the
explanation of how the ozone layer is created and
maintained, studied by Sydney Chapman and
Gordon Dobson, and the explanation of
Photochemical smog done by Haagen-Smit.
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Atmospheric Chem…..21st Century



In the 21st century the focus shifted again. Atmospheric
Chemistry is increasingly studied as one part of the Earth
system.
Instead of concentrating on atmospheric chemistry in
isolation the focus is now on looking it as one part of a
single system with the rest of the other parts of the Earth
systems namely, hydrosphere, biosphere and
geosphere.
In summary- the environmental chemistry studies the
Earth’s system –composed of Air (atmo-), water (hydro-),
land (geo-) and living organisms (bio-).
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Atmospheric


st
Chem…..21
Century
The links between chemistry and climate
such as the effects of changing climate due
to ozone changes.
Interaction of the composition of the
atmosphere with the oceans and terrestrial
ecosystems.
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Methods for studying of Atmosphere

Observations, lab measurements and modelling are
the three central elements in atmospheric chemistry.

For example, observations may tell us that more of a
chemical compound exists than previously thought
possible. This will stimulate new modelling and
laboratory studies which will increase our scientific
understanding to a point where the observations can
be explained.
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Observations


Routine observations of chemical composition tell us
about changes in atmospheric composition over
time.
One important example of this is the Keeling Curve a series of measurements from 1958 to today which
show a steady rise in of the concentration of Carbon
Dioxide. Observations of atmospheric chemistry are
made in observatories such as that on Mauna Loa
and on mobile platforms such as aircraft (e.g. the
UK's Facility for Airborne Atmospheric
Measurements), ships and balloons.
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Keeling Curve: Changes in CO2
Figure: The rise of carbon dioxide as measured by
Charles D. Keeling and collaborators on the top of Mauna Loa.
The unit “ppm” stands for “parts per million by volume.”
The rise results from burning of fossil fuels, with some
contribution from deforestation and production of cement.
http://earthguide.ucsd.edu/globalchange/keeling_curve/01.html
Continued…….observations

Observations of atmospheric composition are
increasing made by satellites with important
instruments such as GOME and MOPITT giving
a global picture of air pollution and chemistry.

GOME (Global Ozone Monitoring
Experiment)
MOPITT is the first instrument to
simultaneously monitor two important
atmospheric chemical species, carbon
monoxide (CO) and methane (CH4).

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Continued…….observations



Surface observations have the advantage that
they provide long term records at high time
resolution but are limited in the vertical and
horizontal space they provide observations from.
Some surface based instruments e.g. LIDAR
can provide concentration profiles of chemical
compounds and aerosol but are still restricted in
the horizontal region they can cover.
Many observations are available on-line in
Atmospheric Chemistry Observational
Databases.
Light Detection And Ranging
•Light
Detection And Ranging) is an optical remote
sensing technology that measures properties of
scattered light to find range and/or other information
of a distant target. The prevalent method to
determine distance to an object or surface is to use
laser pulses.
•Like the similar radar technology, which uses radio
waves, the range to an object is determined by
measuring the time delay between transmission of a
pulse and detection of the reflected signal.
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Lab measurements




Measurements made in the laboratory are essential
to our understanding of the sources and sinks of
pollutants and naturally occurring compounds.
Lab studies tell us which gases react with each
other and how fast they react.
Measurements of interest include reactions in the
gas phase, on surfaces and in water.
Photochemistry which quantifies how quickly
molecules are split apart by sunlight and what the
products are the rates of reaction from
thermodynamic data such as Henry's law
coefficients.
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Durban. [email protected]
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Modeling



In order to synthesize and test theoretical
understanding of atmospheric chemistry, computer
models are used.
Numerical models solve the differential equations
governing the concentrations of chemicals in the
atmosphere. They can be very simple or very
complicated.
One common trade off in numerical models is
between the number of chemical compounds and
chemical reactions modeled versus the
representation of transport and mixing in the
atmosphere.

JC Ngila, UKZN, Chemistry Westville
Durban. [email protected]
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Contid…Models…

Models can be used to interpret observations,
test understanding of chemical reactions and
predict future concentrations of chemical
compounds in the atmosphere.

One important current trend is for
atmospheric chemistry modules to become
one part of earth system models in which the
links between climate, atmospheric
composition and the biosphere can be
studied.
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Characteristics of the Atmosphere
xxhere

Atmospheric science deals with the following:
i.
ii.
iii.
Movement of air masses in the atmosphere
Atmospheric heat balance
Atmospheric chemical composition and
reactions
In order to understand atmospheric chemistry and
air pollution, it is important to have an overall
appreciation of the atmosphere, i.e



Its composition
Physical characteristics
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Atmospheric Composition: based on dry Atmsphere
ppm=mg/Kg
Major compnt
Minor compnt
Noble gases
ppmv
= parts per million by volume
Gas
% composition
Nitrogen, N2
78.084
Oxygen, O2
20.946
Water vapour
0.1-5%
Gas
% or ppmv
Argon
0.934%
Carbon dioxide, CO2
0.035%
Neon, Ne
18.18ppmv
Krypton, Kr
1.18 ppmv
Helium, He
5.24 ppmv
Xenon, Xe
0.087 ppmv
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LECTURE 3
Variation of Atmospheric Pressure & Density
with Altitude



The density of atmosphere decreases sharply with
increase in altitude due to gravity laws & varying
composition of atmosphere in different regions.
More than 99% of total mass of atmosphere is
found within approx 30km (`20miles) of the Earth’s
surface. Query-which part of atmosphere is this?
Total mass of global atmosphere is 5.14x1015
metric tons. This is only a millionth of the Earth’s
total mass. Earth’s mass ~5.14x1021 metric tons.
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Atmospheric Pressure

The atmospheric pressure at any given height is given by:
Ph = Poe-Mgh/RT
Ph = pressure at any height.
Po = Atmospheric pressure at Sea level
= 101325 Pa or Kg.m 1.s2
M = average molecular mass of air molecules in
troposphere = 28.97g/mol = 0.029Kg/mol
g = acceleration due to gravity = 9.81 m.s-1 at sea level
R = gas constant = 8.314 J.mol-1.K -1
T = Temperature in Kelvin (K)
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ENERGY AND MASS TRANSFER IN THE
ATMOSPHERE



The physical and chemical characteristics of the
atmosphere and critical heat balance of the earth
are determined by energy and mass transfer
processes in the atmosphere.
About half of the solar radiation entering the
atmosphere reaches the earth’s surface either
directly or indirectly after scattering by clouds,
atmospheric gases or particles.
The remaining half is either directed back or
absorbed in the atmosphere and its energy
radiated back into the space at a later time as
infrared radiation.
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Contid…Energy & Mass Transfer….




Energy transport which is important in radiating back
into space is crucial and is accompanied by three
major mechanisms, namely:
Conduction:- occur through interaction of adjacent
atoms or molecules without the bulk movement of
matter
Convection:- involves movement of whole masses of
air which may be relatively cold or warm
Radiation:- occurs thro’ electromagnetic radiation in
the infra-red region
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ANTHROPOGENIC CHANGES IN THE
ATMOSPHERE

Ever since life appeared on earth, the
atmosphere has been influenced by the
metabolic processes of living organisms.

For example: carbon dioxide is consumed by
photosynthesis reaction and oxygen is
produced. Oxygen reacts with metal ions such
as iron (II) to produce iron oxides
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Chemical Oxygen demand

Iron oxide deposits, is proof that oxygen is being
consumed.
CO2 + H2O + hν
Fe2+ + O2 + 4H2O
→
CH2O + O2
Oxygen production
→
2 Fe2O3 + 8H+
Metal oxide formation

If plants are abundant, then oxygen is
accumulated => formation of an ozone shield
against solar ultra-violet radiation.

Ozone shield protects the earth from harsh solar
radiation which otherwise would destroy plants,
aquatic life and animals.
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ANTHROPOGENIC ACTIVITIES THAT
DESTROY OZONE LAYER
i) Industrial activities which emit a variety of atmosphere pollutants
including
 SO2
 Particulate matter
 Photochemically reactive hydrocarbons
 Chlorofluoro carbons and inorganic substances

such as toxic heavy metals
ii) Burning of large quantities of fossil fuel which can introduce CO2,
CO, SO2, NOx, hydrocarbons such as CH4 and particulate soot,
polycyclic aromatic hydrocarbons and fly ash into the
atmosphere.
iii) Alteration of land surface-e.g deforestation; burning biomass and
vegetation
iv) Agricultural practices which produce methane from digestive
tracts of domestic animals and water logged anaerobic soils and
nitrogen oxide from bacterial denitrification of nitrates in fertilized
soils.
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MAJOR EFFECTS OF HUMAN ACTIVITIES ON
ATMOSPHERIC CHANGES




Increased acidity
Elevated levels of infrared absorbing gases,
that is, greenhouse gases
Threats to the UV-filtering ozone layer in the
stratosphere.
Increased corrosion of materials induced by
atmospheric pollutants
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GREENHOUSE GASES AND GLOBAL
WARMINGxxhere 10feb

Greenhouse gases are those gases that absorb
infrared radiation. This way they allow incoming
solar radiation energy to penetrate the earth’s
surface while re-absorbing IR radiation.

Examples of greenhouse gases: carbon dioxide,
methane and chlorofluorocarbons absorb IR
radiation and thus retail heat.
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Conti….Greenhouse gases

Greenhouse gases are components of the
atmosphere that contribute to the greenhouse effect.

Without the greenhouse effect the Earth would be
uninhabitable. The mean temperature of the earth
would be about −19 °C (−2 °F, 254 K) rather than the
present mean temperature of about 15 °C (59 °F, 288
K)]. Greenhouse gases arranged in the order of
relative abundance: (i) water vapour, (ii) carbon
dioxide, (iii) methane, (iv) nitrous oxide, and (v)
ozone.

Greenhouse gases come from natural sources and
human activity.
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Lecture 4
The "greenhouse effect"



When sunlight reaches the surface of the
Earth, some of it is absorbed and warms the
surface.
Because the Earth's surface is much cooler
than the Sun, the Earth radiates energy at
much longer wavelengths than the Sun does,
showing maximum peak in the infrared at
about 10µm.
The atmosphere absorbs these longer
wavelengths more effectively than it does the
shorter wavelengths from the sun.
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Conti…Greenhouse effect




The absorption of this long wave radiant energy
warms the atmosphere;
The atmosphere is also warmed by transfer of
kinetic energy and latent heat from the surface.
Greenhouse gases also emit long wave radiation
both upward to space and downward to the surface.
The downward part of this long wave radiation
emitted by the atmosphere is the "greenhouse
effect.".
JC Ngila, UKZN, Chemistry Westville
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Conti…greenhouse effect





The greenhouse effect is the process in which the emission of
infrared radiation by the atmosphere warms a planet's surface.
The name comes from an incorrect analogy with the warming of
air inside a greenhouse compared to the air outside the
greenhouse.
The greenhouse effect was discovered by Joseph Fourier in 1824
and first investigated quantitatively by Svante Arrhenius in 1896.
The Earth's average surface temperature of 15 °C (59 °F) is about
33 °C (59 °F) warmer than it would be without the greenhouse
effect.
Global warming, a recent warming of the Earth's lower
atmosphere, is believed to be the result of an enhanced
greenhouse effect due to increased concentrations of greenhouse
gases in the atmosphere.
NB. In addition to the Earth, Mars and Venus have greenhouse
effects.
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Infrared Absorption by Greenhouse Gases


Infrared (IR) radiation is electromagnetic radiation of
a wavelength longer than that of visible light, but
shorter than that of microwaves. The name means
"below red" (from the Latin infra, means "below"), red
being the color of visible light with the longest
wavelength.
Infrared radiation has wavelengths between about
750 nm and 1 mm (1000,000 nm), spanning five
orders of magnitude. Question. What energy in kJ/mol
does this radiation correspond to?
E=hν= h C/ = 6.63 x 10-34Js x 3.00 x 108m.s-1 /750 x 10-9 m = 2.652
x10-19J/photon x 6.022 x 1023 /mol x 10-3kJ/J = 159.7kJ/mol to
0.12kJ/mol

Humans at normal body temperature can radiate IR
radiation at a wavelength of 10 microns (10,000 nm =
11.98 kJ/mol).
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53
IR Absorption


At the atomic level, infrared energy elicits
vibrational modes in a molecule through a
change in the dipole moment, making it a
useful frequency range for study of these
energy states.
Infrared spectroscopy examines absorption
and transmission of photons in the infrared
energy range, based on their frequency and
intensity.
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Conti….IR




The infrared portion of the electromagnetic spectrum
is divided into three regions; the near-, mid- and farinfrared, named for their relation to the visible
spectrum.
The far-infrared, approximately 400-10 cm-1 (1000–
30 μm), lying adjacent to the microwave region, has
low energy and may be used for rotational
spectroscopy.
The mid-infrared, approximately 4000-400 cm-1 (30–
1.4 μm) may be used to study the fundamental
vibrations and associated rotational-vibrational
structure.
The higher energy near-IR, approximately 140004000 cm-1 (1.4–0.8 μm) can excite overtone or
harmonic vibrations.
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……………IR



Infrared spectroscopy exploits the fact that
molecules have specific frequencies at which they
rotate or vibrate corresponding to discrete energy
levels.
These resonant frequencies are determined by the
shape of the molecular potential energy surfaces,
the masses of the atoms and, by the associated
vibronic coupling.
In order for a vibrational mode in a molecule to be IR
active, it must be associated with changes in the
permanent dipole of a molecule.
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IR …..in simple molecules

The resonant frequencies of the molecules
can be in a first approach related to the
strength of the bond, and the mass of the
atoms at either end of it.

The frequency of the vibrations can be
associated with a particular bond type.

Simple diatomic molecules have only one
bond, which may stretch.
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Example-vibration of molecules18Feb

For example, the atoms in a CH2 group, commonly
found in organic compounds can vibrate in six
different ways: symmetrical and antisymmetrical
stretching, scissoring, rocking, wagging and
twisting:
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IR...complex molecules



More complex molecules have many bonds, and
vibrations can be conjugated, leading to infrared
absorptions at characteristic frequencies that may
be related to chemical groups.
The infrared spectra of a sample is collected by
passing a beam of infrared light through the sample.
Examination of the transmitted light reveals how
much energy was absorbed at each wavelength.
This technique works almost exclusively on samples
with covalent bonds.
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59
LECTURE 5
PROCESSES FOR CATALYTIC
DECOMPOSITION OF OZONE
Ozone Destruction catalysts
There are several catalytic routes that lead to
removal of ozone in the stratosphere. Many
of the processes share a general mechanism
as follows:
X + O3
→ XO + O2
XO + O → X + O2
__________________________
O + O3
→ 2O2 Net reaction
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Conti…..Catalytic Decomposition of
Ozone

The most important of the catalytic species have
been identified to be free radicals and are
symbolized in three categories
●H , ●OH, HOO●
HOx
=
●NO , ●NO
NOx
=
2
●Cl , ClO●
ClOx
=
NB: Depending on the altitude and the mixing ratio,
each of these species has varying ability to destroy
Ozone.
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For example:



HOx at 50km altitude near the stratopause,
account of 70% of total mechanism of
ozone depletion
NOx at 30km near the lower side of
stratosphere, account for mechanism for
removal of most of the ozone. NOx also
catalytic cycle account for 70% of ozone
destruction near tropopause.
ClOx catalytic cycle is said to account for
ozone destruction around 30km altitude
together with NOx.
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62
CATALYSIS BY HYDROGEN-CONTAINING
SPECIES: HOX



This set of catalytic reaction depends on the
availability of a source of oxygen atom to
combine with excess oxygen molecules.
Water and Methane are the most important of
these.
However the temperature in the tropopause is
about -50◦C. At this temperature water is frozen
in crystals and in that form cannot cross to the
stratosphere at which region the Ozone layer is
found.
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Methane as source of hydrogen for
catalytic destruction
Due to freezing of water at low temperature, majority of
reactions use methane to supply the hydrogen which
combines with oxygen to form water. The water then
participates in the following reactions to produce HOx
radicals:
O(1D) + H2O
→
2 ●OH
where O(1D) = excited oxygen atom
●H + ●OH
H2O + hν →
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Hydrogen & Hydroxyl catalysts

The hydroxyl radical can then catalytically decompose ozone as
described by the general cycle in reaction.
●OH + O →
●+O
HOO
3
2
●
●
∙ OH + O
HOO + O →
2
__________________________________
O + O3
→
2O2
Net Reaction

Hydrogen radical also participates in ozone destruction catalysis as
follows
●H + O
●OH + O
→
3
2
●OH + O
●H + O
→
2
_________________________________
O + O3
→
2O2
Net Reaction
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NOTE:

While production of hydroxyl radicals is largely
due to natural causes, it is however influenced
by availability of methane from tropospheric
sources which in turn are affected by human
activities.
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66
LECTURE 6
CATALYSIS BY NITROGEN-CONTAINING
SPECIES: NOX



NOx (mainly NO and NO2) are found in the troposphere
as a consequence of being produced by combustion
processes; heating power plants, vehicles, etc.
NO and NO2 radicals have very short life time, about 4
days and are very soluble in water, hence are converted
into nitric acid and removed in rainfall. As a
consequence, only a small fraction persists in the
troposphere which migrates to the stratosphere where
the ozone layer is found.
Nitrous oxide, N2O is said to be the main source of NOx
in the stratosphere.
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Conti………NOx
At altitudes less than 30km, nitrous oxide can react with
excited state atomic oxygen O(1D), to produce nitric
oxide, NO.
N2O + O(1D) →
2NO
NB. It should be noted that N2O is not a radical and does
not absorb visible light to photolyze. It is not watersoluble. It is therefore very stable and has residence time
of about 120 yrs.
N2O originates from water and soil environments originating
from N- based fertilizers.
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Reactions of nitric oxides
Reactions of nitric oxides are as follows:
NO + O3 →
NO2 + O2
NO2 + O →
NO + O2
____________________________
O + O3
→
2O2
Net Reaction
NB: nitric oxide, NO, reacts with hydroxyl radicals to
produce nitrous acid.
●NO + ●OH + M
→
HNO2 + M
Recall that both ●NO and ●OH are radicals that can
catalyze the destruction of Ozone.
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CATALYSIS BY CHLORINECONTAINING SPECIES: ClOX



Chlorine and Chlorine-containing radicals (●Cl
and ClO● and their bromine analogues) are the
most reactive of all the stratospheric species that
catalyze ozone destruction.
Sources of ClOX are anthropogenic as well as
natural.
The most important natural source is methyl
chloride, CH3Cl. The latter is produced by
biological reactions as well as burning of
vegetation and from volcanic emissions. It is
transported to the troposphere and then
stratosphere.
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Conti……ClOX

Once in the stratosphere region, CH3Cl photolyzes to
release the reactive atomic chlorine and methyl radicals.
●CH + ●Cl
CH3Cl + hν
→
3
where hν = UV radiation energy
NB. Some of the methyl chloride is destroyed before
reaching the stratosphere as follows:
●CH Cl + H O
CH3Cl + ●OH
→
2
2
The ozone destruction mechanism involving atomic
chlorine can be described in the following sequence.
●Cl + O
●ClO + O
→
3
2
●
●
ClO + O
→
Cl + O2
_______________________________
O + O3
→
2O2
Net Reaction
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Other catalytic species
Other catalytic cycles include:
HOO● + ClO●
→
HOCl + O2
HOCl + hν
→
HO● + ●Cl
●Cl + O
●+O
→
ClO
3
2
●OH + O
●+O
→
HOO
3
2
___________________________________
2O3
→
3O2
Net Reaction
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Bromine containing radicals
BrO● + ClO● →
●Br + O
3
●Cl + O
3
●Br + ●Cl + O
2
●BrO + O
→
→
2
ClO● + O2
__________________________________
2O3
→
3O2
Net Reaction
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73
CHLOROFLUOROCARBONS (CFC’s) or
FREONSxxhere



CFCs are used as refrigerant fluids, solvents, aerosol
propellants and blowing agents in the fabrication of foam
plastics.
CFCs are very stable and can exist in the atmosphere for
years.
The photochemical dissociation of CFCs by intense
ultraviolet radiation is given as:
CF2Cl2 + hν → ∙Cl + ∙F+ CClF
(1)
Equation 1 yields chlorine atoms each of which can go
through chain reactions, particularly the following:
●Cl + O
●+O
→
ClO
(2)
3
2
ClO● + O →
Cl● + O2
(3)
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Conti….
CHLOROFLUOROCARBONS (CFC’s)

The effects of reactions (1)-(3) is catalysis of the
destruction of several thousands of molecules of O3 for
each Cl atom produced.

Because of their widespread use and persistency, the
two CFCs of most concern in ozone destruction are
CFC-11 and CFC-12, CFCl3 and CF2Cl2, respectively.

Even in the intense ultraviolet radiation of the
stratosphere the most persistent chlorofluorocarbons
have lifetimes of the order of 100 years.
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“Antarctic Ozone Hole”


The most prominent instance of ozone layer destruction
is the so-called “Antarctic Ozone Hole”. This
phenomenon is manifested by the appearance of
severely depleted stratospheric ozone (up to 50%) over
the polar during the antarctic’s late winter and early
spring.
The depletion of ozone is caused by NO2 reacting with
the radical ● ClO produced in the chlorine-radical attack
of ozone. The reaction is as follows:
ClO + NO2 =
ClONO2
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Ozone-destroying atomic chlorine


The series of reactions that liberate ozone-destroying
atomic chlorine are as follows:
ClONO2 + H2O →
HOCl + HNO3
ClONO2 + HCl →
Cl2 + HNO3
HOCl + hν
→
HO● + Cl●
Cl2 + h ν
→
Cl● + Cl●
Liberation of chlorine atom will propagate the chain
process causing more ozone destruction.
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77
PHOTOCHEMICAL SMOG (PCS)
Origin of the term Smog
The term "smog" was first coined by Dr. Henry
Antoine Des Voeux in his 1905 paper presented
in a meeting of the Public Health Congress in
London, entitled “Fog and Smoke.
Smog is a concern in most major urban centres but,
because it travels with the wind, it can affect
sparsely populated areas in the countryside as
well.
Smog is caused by a reaction between sunlight and
emissions mainly from human activity.
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Conti…..photochemical smog
Photochemical smog is the chemical reaction of sunlight,
nitrogen oxides (NOx) and volatile organic compounds
(VOC's) in the atmosphere, which leaves airborne
particles (called particulate matter) and ground-level
ozone.
*Nitrogen oxides are released in the exhaust of fossil fuelburning engines in cars, trucks, coal power plants, and
industrial manufacturing factories.
VOC's are vapors released from anthroprogenic sources
(man made) like gasoline, paints, solvents, pesticides, and
biogenic sources, such as pine and citrus tree emissions.
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Conti…..photochemical smog




Smog can form in almost any climate where industries or
cities release large amounts of air pollution.
However, PCS is worse during periods of warmer,
sunnier weather when the upper air is warm enough to
inhibit vertical circulation.
PCS is especially prevalent in geologic basins encircled
by hills or mountains.
PCS often stays for an extended period of time over
densely populated cities or urban areas, such as London,
Los Angeles, Mexico City, Houston, Toronto, Athens,
Beijing, Hong Kong, the Randstad or Ruhr Area and can
build up to dangerous levels. What about Johannesburg?
Source: http://en.wikipedia.org/wiki/smog
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Case study-London Smog..



The Great Smog of 1952 darkened the
streets of London and killed approximately
4,000 people in the short term (a further
8,000 died from its effects in the following
weeks and months).
Reluctant to admit that coal smoke was to
blame, the British government initially blamed
a flu epidemic.
In 1956 the Clean Air Act introduced
smokeless zones to the capital, London.
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Conti…. London Smog



Later in London, only smokeless fuels could be
used in these areas.
Consequently, reduced sulphur dioxide levels
made the intense and persistent London smog
a thing of the past. It was after this that the
great clean-up of London began and buildings
recovered their original stone façades which,
during two centuries, had gradually blackened.
Smog caused by traffic pollution, however,
does occur in modern London.
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Natural causes of Smog
Smog can also be due to natural causes that are not
anthropogenic.
Examples:
 An erupting volcano can also emit high levels of
sulphur dioxide, creating volcanic smog, or vog.
 The burning of forests in Indonesia has on a number
of occasions created prolonged smog-like haze,
which have extended to parts of Malaysia,
Philippines, Singapore, Thailand, Sydney, and
California although a lot of the times these fires are
started by farmers who want to clear away land for
the start of the new planting season.

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The Chemistry of Photochemical Smog


The atmospheric smog varies with time of the
day. See Figure-4.2 (page 75) sequence of
chemical species appearing during a
photochemical smog event.
In the morning at 6.00am, the motor traffic
takes to the street and a simultaneous
increase in the atmospheric concentrations of
volatile hydrocarbons and nitric oxide, NO, is
observed. Nitric oxide concentration rapidly
reaches a maximum and then decreases while
at the same time the nitrogen dioxide
concentration fall off and elevated levels of
oxidizing agent and aldehydes are detected.
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Conti……chemistry…PCS


In the evening, a similar pattern is observed
but generally the atmospheric concentrations
are relatively lower.
The concentrations drop to background levels
and remain constant during the night. The
smog consisting of a mixture of: partially
oxidized hydrocarbons, ozone and other
oxidants
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Effects of Smog

In the evening, a similar pattern is observed but
generally the atmospheric concentrations are
relatively lower.The concentrations drop to
background levels and remain constant during the
night.

The smog consisting of a mixture of: partially oxidized
hydrocarbons, ozone and other oxidants.

Smog causes eye irritation, adversely affect plant
growth and are implicated in serious ecotoxicological
problems.
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The Chemistry of Hydroxyl Radical
Production
The
chemical reactions that lead to smog
formation, centre around the hydroxyl radical.
Hydroxyl
radical formation takes place via a reaction
sequence that begins with the production of nitric
oxide, NO.
N2 + O2 ⇄
2NO
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Oxidation of Hydrocarbons

Internal combustion are the main source of
unburned volatile hydrocarbons. They are
oxidized through reactions initiated by
hydroxyl radicals.
Example
●OH + RCH ⇢ ●CRH + H O
3
2
2
where RC∙H2 is alkyl
●CRH + O + M ⇢ RCH OO● + M
2
2
2
where RCH2OO● = peroxyalkyl
RCH2OO● + NO ⇢ RCH2O ● + NO2
where RCH2O● ∙ = alkoxyl
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Conti…. Oxidation of Hydrocarbons
RCH2O● + O2
⇢
RCHO + HOO●
where RCHO = aldehyde
HOO● + NO
⇢ NO2 + ●OH
where HOO● = hydroxyperoxyl
The sum of the above reactions is
RCH3 + 2O2 + 2NO● ⇢RCHO● + 2NO2 + H2O
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Termination reaction-removal of hydroxyl
The terminating reactions aim to remove hydroxyl
from atmosphere as follows:
●OH + ●NO + M
⇢ HNO3 + M
2
HOO● + HOO●
⇢ H2O2 + O2
●OH+ HOO●
⇢ H2O + O2
NB: The products of these reactions are relatively
stable. Nitric acid and hydrogen peroxide are
water-soluble and are removed from atmosphere
through precipitation.
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The Nature of Photochemical Smog




A number of chemicals are present at elevated
atmospheric
concentrations
during
a
photochemical smog event.
Some of the chemicals are gases while others
particularly aldehydes exist as liquid droplets in
form of aerosols. This is the cause of the hazy
appearance present during an intense smog.
The yellowish colour is due to nitrogen dioxide.
Peroxyacetic
nitric
anhydride
(PANS)
CH3C(O)OONO2 are the main cause of eye
irritation. PANS are stable and can be transported
over long distances by air currents.
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Typical Concentrations of some smog
chemicals
Carbon monoxide: 10,000-30,000 ppbv in polluted area but
< 200ppbv in unpolluted areas
Nitrogen dioxides: 100-400 ppbv in polluted areas but <20
ppbv in unpolluted areas
Hydrocarbons: 600-3000ppbv in polluted <300 ppbv in
unpolluted areas
Ozone: 50-150 in polluted but <5 ppbv in unpolluted
Peroxyacetic nitric anhydride (PAN)
50-250ppbv in polluted but <5 ppbv in unpolluted areas.
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ACID RAINxxhere



“Acid rain" is a broad term referring to a mixture of wet
and dry deposition (deposited material) from the
atmosphere containing higher than normal amounts of
nitric and sulfuric acids.
The precursors or chemical forerunners of acid rain
formation result from both natural sources, such as
volcanoes and decaying vegetation and man-made
sources, primarily emissions of sulfur dioxide (SO2) and
nitrogen oxides (NOx) resulting from fossil fuel
combustion.
Acid rain is particularly damaging to lakes, streams, and
forests and the plants and animals that live in these
ecosystems.
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Wet Deposition


Wet deposition refers to acidic rain, fog and
snow.
If the acid chemicals in the air are blown into
areas where the weather is wet, the acids can fall
to the ground in the form of rain, snow, fog, or
mist.
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Dry Deposition

In areas where the weather is dry, the acid
chemicals may become incorporated into dust or
smoke and fall to the ground through dry
deposition sticking to the ground, buildings,
homes, cars, and trees. Later they when moisture
content increases, acid solution is produced.
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DRY AND WET DEPOSITION
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ACID RAIN CHEMICALS IN THE
TROPOSPHERE






Nitrogen oxides, NOx and sulfur compounds (source of SOx) are
the main source of acid rain.
Nitrogen species:
e.g NOx : the sources are fossil fuel, biomass and combustion
Ammonia, NH3: sources are animal excreta, fertilizers and
microbiological release.
Sulfur Species
SO2- from fossil fuel & sulfur ore smelting
Hydrogen sulfide, H2S, carbon disulfide CS2, : from wetlands and
submerged soils
Dimethylsulfide, (CH3)2S, carbonyl sulfide, COS, methyl mercaptan,
CH3SH and Dimethyl disulfide, CH3SSCH3. The sources are mainly,
ocean and soils.
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ATMOSPHERIC PRODUCTION OF
NITRIC ACID
The principle reaction sequence contributing to
production of nitric acid starts with nitric oxide, NO
from combustion processes.
Nitric oxide Chemistry: Daytime
 At daytime, NO is oxidized by O2, O3 or ROO as
follows:
NO


+ O3
→
NO
2
+ O2
When ∙NO2 combines with OH in the presence of a
catalyst, M, nitric acid is produced
NO
2
+ OH + M → HNO3 + M
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Nitric acid Production at Night

At night, production of nitric acid involves
nitrate radical formation from nitrate radical
as follows:
NO +O
NO + O
→
2
3
3
2
NO + NO
NO + NO + O
→
3
2
2
2
NO + NO
→ 2 NO2
3
The formed NO2 react with hydroxyl radical to
produce nitric acid
NO + OH + M
→ HNO3 + M
2
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Reactions of NO3 with olefin
hydrocarbons
Reactions of NO3 with olefin hydrocarbons:
NO + C H
C H NO
→
3
n 2n
n 2n
3
Further reaction of alkyl with nitrate radical :
NO + RCHO →
 + HNO
RCO
3
3
NO + RH
R +HNO
→
3
3
NO + NO
⇄ N2O5
3
2
N2O5 + H2O
→ 2HNO3
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Removal of Nitric Acid

Nitric acid is removed from the atmosphere by
either wet or dry deposition and it is one of
the main contributors to precipitation of acid.

Nitric acid reacts with ammonia as follows:
NH3 + HNO3

→
NH4NO3
The ammonium nitrate, NH4NO3 can act as a
condensation nucleus for the formation of a
water droplet or it can be deposited as part of
the solid aerosol.
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Atmospheric Production of Sulfuric Acid
Oxidation of reduced sulfur species



Production of sulfuric acid is more
complex than that of nitric acid as the
starting materials cover a wide range of
reduced sulfur and partially oxidized
sulfur compounds.
These include hydrogen sulfide, carbon
disulfide,
carbonyl
sulfide,
methyl
marcaptan, and dimethyl sulfide.
All these compounds contain sulfur in its
oxidation state (-2).
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Sequence of Reactions of Sulphur Cmpds

Once sulfur compounds are in the air, a
sequence of reaction begin as follows:
H2S + OH
CS2 + OH
COS + OH
→
→
→
H2O + SH
COS + SH
CO2 + SH
NB: The above reactions release thionyl
radical, SH as the initial product.
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Conti…reactions of Sulphur cmpnds
Hydrogen sulfide and carbon disulfide unlike
carbonyl sulfide, are very reactive and
therefore are quickly consumed.

Further oxidation of thionyl radical leads
to production of sulfur dioxide as follows:
SH
+ O2
SH + O
3
SHO + O
2
→
→
→
SO + OH
SHO + O2
SO + HOO
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Conti…Reactions of Sulphur….
Sulfur monoxide, SO released from above, reacts with
either O2, O3 or NO2 to give SO2 and other products.
2SO + O2
SO + O3
SO + NO2
→2SO2
→ SO2 + O2
→ SO2 + NO
NB. SO2 is ultimately converted to sulfuric acid,
H2SO4.
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Coni…Sulphur…

Dimethyl
sulfide
is
produced
by
phytoplankton living in surface waters of the
ocean. It is oxidized by hydroxyl radical
(∙OH) with a final product being sulfuric acid.

Sulfur dioxide SO2 is also released in large
quantities directly into the atmosphere from
sulfide ore smelting and fossil-fuel
combustion.
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Reducing Acid Rain

There are several ways to reduce acid rain
(i.e acid deposition). These range from
government policy to societal changes and
individual action.

The steps involved in reduction of acid
deposition are:
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Conti…Reducing Acid rain
Understand acid deposition’s causes and effects
 understand acid deposition’s causes and effects, and to
track changes in the environment.
 Scientist to collect air, water & soil samples and measure
them for various characteristics such as pH and chemical
composition, and investigate the effects of acid deposition
on human-made materials.
 Scientists to understand the effects of sulfur dioxide (SO2)
and nitrogen oxides (NOx).
 People to understand the process of how acid rain damages
the environment.
 People to find out what changes could be made to the air
pollution sources that cause the problem.
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Steps to solve acid deposition problem
a) Clean up smokestacks and exhaust pipes
NB. Almost all of the electricity that powers modern life
comes from burning fossil fuels such as coal, natural
gas, and oil. Sulfur dioxide (SO2) and nitrogen oxides
(NOx) are the main acid chemicals.


Options for reducing SO2 emissions, include: using
coal containing less sulfur, washing the coal, and
using devices called “scrubbers” to chemically
remove the SO2 from the gases leaving the
smokestack.
Power plants to change type of fuels e.g, burning
natural gas creates much less SO2 than burning
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113
Durban. [email protected]
b) Use alternative energy sources

Other sources of electricity besides fossil
fuels.
They
include
nuclear
power,
hydropower, wind energy, geothermal
energy, and solar energy.

Alternative energies, such as natural gas,
batteries, and fuel cells, available to power
automobiles.
NB: All sources of energy have environmental
costs as well as benefits.
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c) Restore a damaged environment
NB. It takes many years for ecosystems to
recover from acid deposition, even after
emissions are reduced and the rain pH is
restored to normal.
There are some things that people can do to
bring back lakes and streams more quickly.
 Limestone or lime (a naturally occurring basic
compound) can be added to acidic lakes to
“cancel out” the acidity. Liming, has been
used extensively in Norway and Sweden.
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d) Evaluation of the progress made on
acid rain reduction process

If the depositions are reduced, environmental
protection agency (EPA) scientists must
assess the reductions to make sure they are
achieving the anticipated results.

If no changes, to consider additional ways to
reduce emissions that cause acid deposition.
Example: focus on energy efficiency and
alternative energy.
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e) Take action as individuals
NB. It may seem like there is not much that one
individual can do to stop acid deposition.
However, one can do the following:
1. Turn off lights, computers, and other
appliances when you're not using them.
2. Use energy-efficient appliances for lighting,
air conditioners, heaters, refrigerators,
washing machines, etc.
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………..Take action as individuals
3. Use electric appliances only when you need
them.
4. Use public transportation, or better yet, walk
or bicycle whenever possible
5. Buy vehicles with low NOx emissions, and
properly maintain your vehicle.
6. Be well informed.
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THE CHEMISTRY OF URBAN AND
INDOOR ATMOSPHERES
The chemical composition of air in places where people
live including major urban areas around the world and
indoor contaminants vary with modernization or
industrialization of the locality.
Urban areas are likely to be affected by atmospheric
pollution due to the following major factors:
(i) Combustion of fossil fuels in motor vehicles
(ii) In-space heating and cooling
(iii) In-power generation and industrialization
(iv) Incineration of waste materials
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CHEMISTRY OF URBAN AND INDOOR
ATMOSPHERES
Use of petroleum products especially in motor vehicles
result in ground-level emissions of carbon monoxides,
volatile hydrocarbons, nitrogen oxides and sometimes,
lead compounds. These emissions are accompanied by
aldehydes and other secondary pollutants.
The
combustion of biomass and coal produces
substantial concentrations of solid particulate matter
along with nitrogen oxides, polyaromatic hydrocarbon
(PAHs) compounds as well as sulphur dioxide.
Open burning refuse or garbage cause air pollution is a
source of volatile organic carbon compounds and solid
particulate matter (SPM).
Hurricanes and wind are the source of particulate matter
such as dust especially in dry areas.

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POLLUTANTS IN THE URBAN ATMOSPHERE
World Health Organization (WHO) Standards
for Air Quality
 The WHO guidelines for air quality take into
account time period over which measurements is
done. This is known as human exposure.

Potential toxicity depend on both atmospheric
concentration and duration of contact with the
atmosphere. That is;
Exposure = Concentration x time
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Quality guidelines



The quality guidelines must specify the acceptable
concentration to be exposed to humans over a specified
period.
Example: carbon monoxide at 20mg.m-3 (20ppbv) may be
acceptable if exposure time is 1 hour but not acceptable for
longer period times.
For longer exposure such as 8hrs, the allowed concentration
of carbon dioxide should not exceed 10mg.m-3, that is,
0.01ppmv or 10ppbv.
WHO works closely with United Nations Environmental
Program (UNEP) to carry out air quality monitoring.
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Table 1 is a summary of WHO guideline values for air
quality-values in µg.m-3 or parts per trillion in volume (pptv).
Pollutant
Max.
time Averaging time
weighted (µg/.
SPM=Suspended
particulate matter
-3
m )
SO2
500
10 min
CO
30,000
1 hr
NO2
400
1 hr
O3
150-200
1 hr
(black 100-150
24hr
RSP = Respirable
suspended particulate,
PM10 with particle size
TSP
150-230
24hr
< 10µm
RSP; PM10
70
24hr
Pb
0.5-1
1yr
SPM
smoke)
TSP=Total suspended
particulate
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Suspended Particles Matter (SPM)
Concentration
of atmospheric particulates is
severe in some megacities (cities > 10million
population) and average levels may range from
200 to 600 µg.m-3 or pptv.
Human
health associated with high values depend
on the nature of particulates.
Examples: those derived from coal and those in the
PM10 or PM2.5 categories, have been shown to be
hazardous.
NB: PM10 is particulate matter size < 10µm ;
PM2.5 < 2.5µm.
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Air quality parameters


Carbon Monoxide (CO): depend on high traffic density – vary from city
to city.
Sulphur dioxide (SO2): Usually produced by coal. Sulfur dioxide conc. is
low in cities that use low coal fuels.

Nitrogen dioxide (NO2): Higher levels expected indoors with poor
ventilation where kerosene or natural gas is used for heating and cooking.

Ozone (O3): from reaction of gases in the troposphere; trace amounts may
result from mass transfer from stratosphere.
Lead (Pb): Airborne lead depends on the population of cars, the
concentration of lead additives in the fuel and availability of unleaded fuel.
Concentrations in leaded gasoline vary between 0.1 and 2.0 g.L-1.
NB. Use of tetraethyl lead to augment the octane number (?) is becoming less.

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Petrol combustion-octane number





Reactions of hydrocarbons (HCs) with
oxygen is the basis for fuels.
Example: octane reacts with oxygen to give
out heat (5480 kJ/mole of HC ); exothermic
rxn.
Some of the HCs burn more smoothly than
others.
Explosive burning results in engine knocking.
The HC; 2,2,4-trimethylpentane (TMP) which
is a structural isomer of octane has octane
rating of 100, i.e excellent performance.
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……………...Octane rating




Heptane (C7H16) has poor engine
performance with octane rating of 0.
A mixture of TMP and heptane in the ratio,
87:13 gives octane rating of 87.
TMP and heptane are the reference values
when assigning octane numbers.
In general, branched chain hydrocarbons
have higher octane numbers than their
straight chain counterparts.
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…….Octane ratinghere 22feb10



Octane rating of gasoline can be improved by
adding anti-knocking compounds to prevent
premature combustion.
Tetraethyllead (C2H5)4Pb has previously
been used as an additive but it has been
phased out in many countries.
Other formulations have been developed
more recently, e.g methylcyclopentadienyl
manganese tricarbonyl (MMT), is added at a
level of 0.1g/L.
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Methylcyclopentadienyl
manganese tricarbonyl
MMT
or MCMT) is an organomanganese
compound with the formula (CH3C5H4)Mn(CO)3.
…….….MMT additive

MMT is in itself toxic but it combusts
completely in the engine, resulting in
combustion products like manganese oxide,
e.g Mn3O4. Manganese is an essential
element for animals and plants.
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………Issue on……… MMT



Marketed initially in 1958 as a supplement to the
gasoline additive tetraethyl lead to increase the
fuel's octane rating, MMT was later used in
unleaded gasoline.
Although banned as a gasoline additive in the
United States from 1977 to 1995, MMT has been
used in Canadian gasoline since 1976 (though
was banned from 1997-1998 due to safety
concerns) and was recently introduced in
Australia.
It is sold under the trade names HiTec 3000 and
AK-33X. It is also marketed as Ecotane by T2
Labs.
INDOOR AIR QUALITY

Many people spent most of their time indoors (home, office,
etc.). The atmospheres encountered indoor vary a great deal.

The materials of house construction may vary from clay-rich
soils or other fresh or baked earth materials.
In some cases, the homes are open and air exchange is rapid
while in others heating may be done over an open fire in a
room without a chimney and also a variety of fuels may be
used.
The building materials may range from bricks, stones, wood,
various plastics and metals.
Activities in the homes include: cleaning, cooking, heating
over open or closed fires with varying smoke conditions.



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Major factors that determine the quality of indoor air






The nature of the ambient air, outdoor around the building
plays a role. In this case, the outdoor atmosphere is influenced
by air outside.
Design and site of the building is important. This will dictate
the quality of exchange of indoor atmosphere.
Nature of materials present in the building such as polymers.
The latter could be a source of formaldehydes or other
partially oxidized organic compounds.
Building materials from clays, concrete, etc., may contain
traces of radioactive elements such as uranium.
Activities that take place inside the house. These may include
combustion of wood for heating, cooking gas, electric
cookers, etc. Cleaning of the house may involve mechanical
devices such as vacuum cleaner, that create dust.
Use of cleaning solvents and detergents, insecticide sprays,
toilet sprays and air fresheners.
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Relationship between indoor and outdoor air quality
■
A general equation describing the steady-state behaviour of a
stable compound with respect to indoor and adjacent outdoor
concentrations of substances, is given below:
Ri = ke Ci - ke Co
where Ri = net rate production of the compound inside the house:
units= concentration per time.
Ci and Co = indoor and outdoor concentrations of the substances in
question
ke = first-order rate reaction constant for atmosphere exchange,
defined as the air exchange rate with units of per time (time-1).

In steady-state, the internal concentrations are given
by: Ci = Co + Ri / ke.

If outdoor air contribution is negligible, then Ci = Ri /ke.
If none of the chemicals is produced indoor, then Ci = Co

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CALCULATION ON INDOOR AIR QUALITY
Ref: Environ Chem: A global perspective by vanLoon
& Duffy (2005); page 153



Question: Concentration of indoor levels
Consider a situation where open fire in a well
ventilated home produces VOCs at a rate of 30
mg.m-3.h-1. A complete exchange rate of air takes
place 5 minutes (1/12 h). The ambient outdoor
concentration of VOCs is 75 µg.m-3. Calculate the
indoor concentration of these compounds..
Use the equation: Ci = Co + Ri / ke.
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Conti…………
Solution
 Step 1: First calculate the first order reaction rate ke,
the air exchange rate with units of time-1, i.e, 1/time.
time = 1/12 h, therefore, 1/time = 12h-1

Step 2: Next: Given Ri , the net reaction of production
in a well ventilated home = 30mg.m-3.h-1, convert mg
to µg but keep m-3.h-1. Since 1 mg = 1000 µg, then
30 mg = 30,000µg

The rate of production of VOCs, Ri =30 mg.m-3.h-1
= 30,000µg.m-3.h-1
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Conti………Solution
Step 3: Given the ambient outdoor concentration of VOCs
Co = 75 µg.m-3, you can calculate the indoor concentration:
Step 4: The indoor concentration of VOCs
Ci = Co + Ri / ke
Substitute for the terms on the right hand side of the
equation:
Ci = 75 µg.m-3 + 30,000µg.m-3.h-1 / 12h-1
= 75 + 2500 = 2575 µg.m-3
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COMMON INDOOR AIR CONTAMINANTS
Air contaminants refer to levels above the outdoor
background level.
1. Radioactive compounds:
 Radioactivity is usually associated with randon
(Rn) noble gas, released by Uranium isotope 238
and also by Thorium isotope 232 with half-lifes of
4.5 and 14 billion years, respectively. These
elements are found in geological materials such as
rocks and fossils.
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Radioactivity



The spontaneous emission of particles and/or
energy from atomic nuclei.
The spontaneous emission of radiation from
the nucleus of an atom.
Radionuclides lose particles and energy
through this process of radioactive decay.
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Radioactive elements

Radioactive elements, such as uranium (239U)
thorium (234Th) and potassium (40K) break
down (decay) fairly readily to form lighter atoms
e.g Be, B.



The energy that is released in the process is made
up of small, fast-moving particles and high-energy
waves.
These particles and waves are, of course, invisible.
(The level of radioactivity of an element varies
according to how stable its atoms are).
Other elements with naturally occurring radioactive
forms (isotopes) , are carbon (C13), bismuth (210Bi),
radon (223R) and strontium (88Sr).
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Conti… Radioactivity process





Radioactivity is a random process that happens
naturally as the isotopes in particular elements
decay. The isotopes continue to break down over
time.
The length of time that is taken for half of the nuclei
in an element to decay is called its 'half-life'.
A half-life can be very short (milliseconds to hours)
or very long (hundreds of thousands of years).
Radiation also arises from nuclear fission which
can be spontaneous but is usually initiated in a
nuclear reactor.
Fission is a radioactive process; it releases energy
as the heavy nucleus is split into two.
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Example: Calculation of Half-Life of
Radioactive Elements







Consider strontium-90 which has a half-life of
approximately 28 years.
Initially, at time t=0, the sample is 100% strontium-90
After 28 years, only half the original amount of
strontium will remain: ½ x 100% = 50%
After another 28 years, only half of this amount of
strontium-90 will remain: ½ x 50% = 25%
After another 28 years, only half of this amount of
strontium will remain: ½ x 25% = 12.5%
and so on.
At any given time, the amount of strontium-90 that has
undergone decay can be calculated:
Amount of strontium-90 decayed = the original amount the amount remaining.
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Calculations


The amount of radioactive isotope remaining
can be calculated:
Nt = No x (0.5)number of half-lives
Nt = amount of radioisotope remaining
No = original amount of radioisotope
number of half-lives = time ÷ half-life
Example
Calculate the percentage of strontium-90
remaining after 280 years, given its half-life
is 28yrs.
Nt = No x (0.5)number of half-lives
Nt = ? %
No = 100%
number of half-lives = time ÷ half-life = 280 ÷
28 =10
Nt = 100 x (0.5)10 = 0.098%
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Strontium-90 half-lifes
%
%
Number
StrontiumTime Strontiumof Half90 that
(years)
90
lives
has
remaining
decayed
0
0
100
0
1
28
50
50
2
56
25
75
3
84
12.5
87.5
4
112
6.25
93.75
5
140
3.125
96.875
6
168
1.5625
98.4375
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Strontium-90 half-lifes
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2. Volatile Organic Compounds (VOCs)
Sources are:
 Paints: toluene, ethylbenzene, 2-isopropanol and
butanone.
 Cleaning agents: households solvents, detergents.
 Wood-building
materials such as plywood
produce formaldehyde.
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3. Polybrominated diphenyl ether
Polybrominated diphenyl ether (PBDE) is toxic. General
structure is shown below. PBDE is used in commercial
household products such as plastics casings for appliances,
in fabrics used for clothing, carpets, etc.
Chemical structure of PBDEs
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Conti…air contaminants
4. Emissions from indoor combustion.
This is combustion of fuel that contains VOCs;
burning of coal, wood and biomass.
Tobacco smoking is a source of many VOCs
including aldehydes, ketones, organic bases such
as nicotine, organic acids.
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5. Indoor particulates
These include: solid aerosols from dust;
combustion of coal & biomass material.
 Particle size is usually in the range PM10
(<10µm). Particle size <2µm, can easily
enter respiratory track.
 Smoking contributes to respirable particulate
matter inside a building.
 Polyaromatic
hydrocarbons (PAHs) are
emitted from coal & biomass.
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Particles in the atmosphere






Particulate is a term that has come to stand for particles in
the atmosphere.
Particulate matter makes up the most visible and obvious
form of air pollution.
Particles in the atmosphere range from 0.5 mm (size of sand)
down to molecular size level (nanometer).
Particles may consist of either solids or liquid droplets.
Atmospheric aerosols are solid or liquid particles smaller
than 100 µm in diameter.
Pollutant particles in the 1 nm to 10 µm range are commonly
suspended in the air near sources of pollution such as the
urban atmosphere, industrial plants, highways and power
plants.
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DESCRIPTION
PARTICLES
OF
ATMOSPHERIC
Terms
1. Aerosol
Meaning
Colloidal-sized
atmospheric
particle
2. Condensation Formed by condensation of
aerosol
vapors or reactions of gases.
3. Dispersion
Formed by grinding of solids,
aerosol
atomization of liquids or
dispersion of dusts.
4. Fog
Denotes high level of water
droplets
5. Haze
Denotes decreased visibility
due to presence of particles
6. Mists
Liquid particles
7. Smoke
Particles
formed
by
incomplete combustion of fuel
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Nature of particles





Very small solid particles include (1 nm-10 µm ): carbon
black, silver iodide, combustion nuclei, sea-salt nuclei- tend
to be acidic.
Larger particles include (100 µm -500 µm ) : cement dust,
wind blown soil dust, foundry dust and pulverized coal- tend
to be basic.
Liquid particles or mist- include; raindrops, fog and sulfuric
acid mixture.
Particles of biological origin: viruses, bacteria, bacterial
spores, fungal spores and pollen.
Important atmospheric contaminants- mainly inorganic and
organic particles.
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Effects of atmospheric particles
Effects on climate
e.g Aerosols, natural and anthropogenic, can affect
the climate by changing the way radiation is
transmitted through the atmosphere.


Damage buildings: e.g dry acid deposits corrodes
iron/metal roofing materials.

Reduced visibility & causes undesirable effects:
e.g itching of the eyes, breathing problems, etc.
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Conti… Effects of atmospheric particles

All aerosols both absorb and scatter solar and
terrestrial radiation.

If a substance absorbs a significant amount of
radiation, as well as scattering, the substance
is said to be absorbing.

Scattering is quantified as the ratio of
scattering alone to scattering plus absorption
of radiation by a particle.
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Physical behaviour of particles



Small colloidal particles undergo diffusion
processes and coagulate together to form larger
particles.
Mechanism for removal of particles from the
atmosphere is mainly through sedimentation &
scavenging by rain drops and then precipitation.
Particle size refers to diameter of the particle but
in some cases radius may be used.
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Process for particle formation




Physical Process: particle formation is mainly
through disintergration of larger particles > 1 µm.
Many dispersion aeorosols originate from natural
sources: sea-spray, windblown dust, volcanic dust.
Chemical process: Inorganic particles mainly
consist of metal oxides formed by oxidation of the
metal by oxygen.
Organic particles are produced mainly through
internal combustion engines.
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Composition of Inorganic Particles





Aluminium oxide, iron oxide, calcium oxide and
silicon dioxide are due to soil erosion, rock dust, coal
combustion.
Carbon particles- due to incomplete combustion
Sodium and chlorine compounds- due to marine
aerosols
Antimony and selenium- due to combustion of oil,
coal or refuse.
Lead from combustion of leaded fuels & wastes
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Composition of Organic Particles
A wide variety of organic compounds most of which are
toxic: polycyclic aromatic hydrocarbons (PAHs) such as
benzo(a)pyrene, chrysene, benzo-fluoranthene, acridine.
Radioactive particles
 Main source of radionuclides in atmosphere is randon: it is
a noble gas produced from radium decay.
 Cosmic rays in the atmosphere produce radionuclides
which are isotopes of: 7Be , 10Be, 14C, 39Cl, 3H, 22Na, 32P
and 33P
 Nuclear weapons are the main source of radioactive
particulate matter in atmosphere.

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158
Control of Particulate Emissions

Removal of particulate matter from gas streams is
the most practiced means of air pollution control.

Techniques for removal depends on particle size,
loading, nature of particles and type of scrubbing
system.
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Methods of particle removal
These include:
 Sedimentation
and inertia, i.e gravitational
settling as a continuous process.
 Particle filtration using fabric filters that allow
gas molecules to pass through but retain the
particulate matter.
 Scrubbers- this involves use of scrubbing liquid
which forms small droplets for scavenging
particles from the gas stream.
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Air Pollution Control for Particulate
Emissions


It is possible to minimize emissions of aerosol
particles from point of source such as thermal
electrical generating stations or industrial smelting
units.
Containment of particulate matter is achieved using
devises that remove the aerosols from fast moving
stack gas stream. Common collection methods
include: settling chambers, cyclones, fabric filter,
scrubbers, and electrostatic precipitators as shown
in the slides that follow.
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Settling Chambers




Are the simplest and commonly used.
Construction includes variety of baffles and
open space designed to allow the particles
sufficient time to settle under the force of
gravity.
Settling rates are limited by gravity therefore
method effective for large particle size >10µm.
They come in different design. The
mechanism include adsorption and
absorption.
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Absorption Method
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Adsorption
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Combustion
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Fabric Filters: Filtration



Fabric filter or bags operate in a similar principle as
vacuum cleaner.
The air stream is made to pass thro a porous fabric
material and is effective for particulates size in the
range 0.01 - 10µm range.
Bags or fabric filters are sensitive to temperature
and humidity. The fine particles clog the filters and
therefore must be periodically cleaned.
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Filtration
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Electrostatic Precipitator


Electrostatic precipitator causes the particles in a
gas stream to become charged by electrons
produced thro an electrical discharge between
two electrodes.
The negatively charged particles then migrate to
the positive electrode and are collected and
removed from the emission stream. Positively
charged particles move to negative electrode.
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Electrostatic Precipitator
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Scrubbers



Scrubbers allow gas stream to be in contact
with a fine mist or spray of water.
The water droplets capture many small
particles and these settle more rapidly into a
collector container.
Scrubbers come in different designs as
shown below.
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Liquid Scrubber
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Cyclones



Cyclones are cone-shaped devices that cause the
waste gas stream to swirl rapidly in spiral fashion
causing larger particles to move towards the wall of
the cone by centrifugal force.
Once in contact with the wall, the particles slide down
the inner surface of the cone to a collection container
below it.
Stoke’s law determines the extent of removal of
particles but the settling rates can be greatly
enhanced by the increased force due to cyclone
action. In this case removal of particles <10µm can
be achieved.
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Stokes Law
2
( p -  a ) C g d p
t 
18
Where
vt = terminal velocity of particles in m.s-1
pp = density of particle in g.cm-3
Pa = density of air = 1.2 x 103 g.m-3 at Po and 25° C
C = Stokes correction factor for assuming spherical shape and
discontinous of fluid interactions when the particle size is small
compared with the molecular mean path in air.
g = acceleration due to gravity = 9.8 m.s-2
dp = particle diameter in meters and
 = viscosity of air = 1.9 x 10-2 g.m-1.s-1 at P° and 25° C
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Cyclone
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Combustion
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Minimize Emission from point Source:
example SO2

Minimize emissions of aerosol particles from
point of source such as thermal electrical
generating stations or industrial smelting
units.
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EXAMPLE: Sulfur Dioxide Control
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http://www.apt.lanl.gov/projects/cctc/factsheets/puair/adflugasdemo.html
177
INORGANIC AND ORGANIC
WATER POLLUTANTS

Throughout history, the quality of drinking water
has been a factor in determining human welfare.

Water pollutants can be divided into general
classifications as summarized in Table below:
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General Types of Pollutants
Class of Pollutant
Trace elements
Significance
Health, aquatic biota
Metal-organic combinations
Metal transport
Inorganic pollutants
Toxicity, aquatic biota
Asbestos
Human health
Algae nutrients
Eutrophication
Radionuclides
Toxicity
Acidity, alkalinity, salinity (in
excess)
Water quality, aquatic life
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Conti….type of pollutants
Sewage
Taste, odor and color
Biochemical oxygen
demand
Trace Organic Pollutants
Pesticides
Polychlorinated biphenyls
Chemical carcinogens
Petroleum wastes
Pathogens
Detergents
Sediments
Water quality, O2 levels
Esthetics
Water quality, oxygen
levels
Toxicity
Aquatic biota, wildlife
Possible biological effects
Incidence of cancer
Affect wildlife, esthetics
Health effects
Eutrophication, wildlife,
Water quality, aquatic biota,
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Elemental Pollutants
Trace elements
 Trace levels refer to those elements that occur at
very low levels in a given system. Depending on
the instrument, trace concentrations may not be
detectable. Generally, levels in parts per million
or less can be referred to as trace.
 Some trace elements encountered in natural
waters are recognized as nutrients required for
animal and plant life. Of these, many are essential
at low levels but toxic at higher levels
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Heavy Metals here!




These are among the most harmful elements.
Heavy metals are located on the lower right-hand
side of the periodic table. Examples are lead,
cadmium and mercury.
Most of the metals have a tremendous affinity for
sulfur bonds in enzymes.
The mechanism of the biochemical effects of
metals involve reactions of proteins, carboxylic
acid (CO2H) and amino group (NH2) with metals.
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Conti…..Heavy metals





Cadmium, copper, lead and mercury ions bind to cell
membranes hindering transport process.
Heavy metals may also precipitate phosphate
biocompounds or catalyze their decomposition..
Metalloids elements such as arsenic, selenium and
antimony are of interest, e.g selenium is essential.
Inorganic chemical industries have the potential to
contaminate the water with trace elements.
The chemical manufacturing include, chlor-alkaline,
hydrofluoric acid, sodium dichromate, aluminium
fluoride, chlorine pigments, copper sulfate etc, have the
potential to contaminate the environment.
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Toxic Heavy Metals
Cadmium (Cd)
 Sources may be industrial discharge from metal
plating.
 Effects of acute cadmium poisoning include: high
blood pressure, kidney damage, destruction of
testicular tissue, etc.
 Due to similarities of Cd and Zn both (oxidation
+2), cadmium may replace zinc in some enzymes,
thereby altering the stereostructure of the enzyme,
and therefore impairing the catalytic activity of
the enzyme which may result in death.
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Lead




Sources may be from industrial and mining
activities. Lead from gasoline leaded petrol is a
major source of atmospheric and terrestrial lead.
Acute lead poisoning in humans causes severe
dysfunction in the kidneys and reproductive
systems.
Lead may cause mental retardation in those
children exposed to the metal.
Lead poisoning causes anemia
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Mercury





It is found as a trace component of many minerals.
Continental rocks contain around 80 ppb of mercury.
Mercury sulfide, HgS is the main mercury ore.
Hg is used in various apparatus in the science laboratories
such as thermometers.
High concentrations of Hg found in water and fish tissues
results from the formation of soluble monomethylmercury,
CH3Hg+ ion and volatile dimethylmercury, (CH3)2Hg,
formed by anaerobic bacteria in sediments.
Health effects include neurological damage such as:
paralysis, blindness or insanity.
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186
OCCURRENCE AND SIGNIFICANCE OF TRACE ELEMENTS IN
NATURAL WATERS
ELEMENT
SOURCES
EFFECTS &
SIGNIFICANCE
Arsenic
Mining by-product,
pesticides, chemical
waste
Coal, nuclear power,
space industries
Coal, detergent
formulation, industrial
waste
Toxic, possibly carcinogenic
Beryllium
Boron
Acute and chronic toxicity.
Possibly carcinogenic
Toxic to some plants
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WHO
Limit/
ppm
0.05
n/k
1.0
187
Cadmium
Chromium
Copper
Fluorine/
Fluoride
Industrial discharge,
mining waste, metal
plating, water pipes
Replaces zinc biochemically,
cause high blood pressure and
kidney damage, destroys
testicular tissue and red blood
cells, toxic to aquatic biota
Metal plating, cooling- Essential trace element
tower waste additive
(glucose tolerance factor),
(chromate), Cr(VI) in possibly carcinogenic as
wastewater
Cr(VI)
Metal plating,
Essential trace element, not
industrial and domestic very toxic to animals, toxic to
wastes, mining mineral plants and algae at moderate
leaching
levels
Natural geological
Prevent tooth decay at about
sources, industrial
1.0 ppm but causes mottled
waste, water additive teeth and bone damage at
around 5ppm in water.
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0.01
0.05
1.0
0.8-1.7
depend on
the temp
188
Iodine/iodide Industrial waste water, Prevents goiter
natural brine, sea
water, intrusion
Iron
Corroded metal,
industrial waste, acid
mine drainage,
Lead
Industry, mining,
plumbing, coal,
gasoline
Mining, industrial
waste, acid mine
drainage
Manganese
Mercury
Mining, industrial
n/k
rare in
fresh
water
0.05
Essential nutrients
(component of haemoglobin),
not very toxic, damages
materials (bathroom fixtures
& clothing)
Toxicity (anemia, kidney
0.05
disease, nervous system)
wildlife destruction
Relatively non-toxic to
0.05
animals but toxic to plants at
high levels, stains materials,
clothing & bathroom fixtures
Acute & chronic toxicity
Very low
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Molybdenum Industrial waste,
natural sources,
cooling tower water
additive
Selenium
Natural geological
sources, sulfur, coal
Silver
Possibly toxic to animals,
essential to plants
n/k
Essential at low levels, toxic 0.01
at high levels. Possibly
carcinogenic
Causes blue-grey
0.05
discoloration of skin, mucous
membranes, eyes
Natural geological
sources, mining,
electroplating, film
processing waste,
disinfection of water
Zinc
Industrial waste, metal Essential elements in many 5.0
plating, plumbing
metallo-enzymes, aids wound
healing, toxic to plants at
high levels, major component
of sewage sludge
Ref: USA- EPA, Trace elements in waters of the USA, 1975
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NATURAL WATERS
Fresh Water, Natural Composition of Water

Although water has the simple formula H2O, it is
a complex chemical solution. "Pure" water
essentially is nonexistent in the natural
environment.

Natural water, whether in the atmosphere, on the
ground surface, or under the ground, always
contains dissolved minerals and gases as a result
of its interaction with the atmosphere, minerals in
rocks, organic matter, and living organisms.
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Chemical Controls of Water Composition

The acidity of water is gauged by its pH i.e
hydrogen ion (H+); pH = −log(H+).

High conc. H+ in the water, the lower its pH, and
the greater its acidity.

Acid waters have a pH < 7 (neutral pH is 7); acid
waters at pH 1 or less.

Basic (alkaline) waters have a pH > 7 greater than
7; basic waters at pH 14.
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Natural Acidity




Natural rainwater is slightly acidic because it
interacts with carbon dioxide (CO2) in the
atmosphere, forming carbonic acid (H2CO3).
The two reactions in rainwater are as follows:
H2O + CO2 = H2CO3
H2CO3 = HCO3− + H+
A limit exists as defined by the equilibrium
constant of the reaction.
The conc. of carbonic acid depends on how much
carbon dioxide is in the atmosphere.
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Conti…Natural Acidity

The Earth's atmosphere presently contains, on
average, approximately 0.3 percent carbon dioxide.
Using this value in the two reactions above,
hydrologists can calculate the concentration of H+
in rainwater at chemical equilibrium as 10−5.7
moles per liter. This concentration is equivalent to
a pH of 5.7, slightly acidic.

Because pH 7 is neutral, pH 5.7 is considered
slightly acidic.
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Conti…Natural Acidity
Slightly acidic rainwater reacts with land-derived
dust particles in the atmosphere. These reactions
result in the rainwater gaining dissolved calcium
(Ca2+), magnesium (Mg2+), sodium (Na+),
potassium (K+), and other elements.
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Conti…Natural Acidity


Although carbonic acid is a weak acid, it is very
effective over geologic time. Carbonic acid is
largely responsible for the breakdown of rocks to
soil during chemical weathering and the formation
of limestone caverns and sinkholes. The lower the
pH, the more acidic the water, and the more
minerals it can dissolve.
Sea spray, carried aloft by winds blowing across
the ocean, contributes to dissolved constituents in
rainwater. Sea spray is the primary source of
chloride (Cl−) in rainwater and a significant
amount of sodium (Na+).
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Oxidizing–Reducing Reactions

Oxidizing–reducing reactions change the charge of an
ion as it gains or loses an electron. The solubility of
some elements in water depends on whether they are
oxidized or reduced.

Example iron (Fe) can exist either as reduced iron (Fe2+)
or oxidized iron (Fe3+). Iron is more soluble in the
reduced state than it is in the oxidized state: (Fe2O3).

The oxidation of an organic molecule can result in iron,
existing as a solid iron oxide mineral (Fe2O3), being
reduced and there4 dissolve in the water as the reduced
form (Fe2+).
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Streams and Lakes




The composition of stream and lake water varies from
one place to another, and within a single watershed varies
both seasonally and along the stream's path.
The major source of dissolved minerals in streams and
lakes is the rocks the water moves over and through along
its path from where it falls as precipitation to where it
exits the watershed or enters the lake.
As the slightly acidic water encounters rocks, the
minerals begin to dissolve and contribute their elements
to the water.
The type of rocks in the watershed influence stream-water
composition. A stream flowing over sedimentary rocks
will have a different composition than a stream flowing
over igneous rocks.
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Conti… Streams and Lakes



Also contributing to stream-water and lake-water
composition are reactions between the water and the
biomass.
Temperature influences the amount of dissolved
gases (e.g., oxygen).
Stream-water composition changes from headwaters
to outlet because the water is in contact with the
rocks and sediments of the streambed for
cumulatively longer times. Also, tributaries draining
different geologic areas may enter the stream, and
groundwater may seep into the stream.
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Conti… Streams and Lakes

Seasonal variations in stream-water composition may
reflect differing precipitation amounts and stream's flow
that is contributed by groundwater.

In the drier times of the year the proportion of precipitates
in groundwater is greater than in the wet season.

Lake-water composition is influenced by evaporation,
among many other factors. As water evaporates, the
dissolved minerals are left behind.

The more the evaporation, the higher the concentration of
dissolved minerals (salts) in the water or the salts will
precipitate from the solution.
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Surface & Ground water composition16mar

Many of the factors that influence the surface
water composition also influence groundwater
composition.

Groundwater is always in contact with rocks and
minerals and moves more slowly than surface
water in centimeters per day instead of kilometers
per hour. As a result, groundwater often contains
more dissolved minerals than surface water (as is
evident from comparing streams and groundwater
in the table below).
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Element
Calcium
Magnesium
Sodium
Potassium
Bicarbonate
Sulfate
Chloride
Bicarbonate
Sulfate
Chloride
Silica
TDS
pH
1 2 3 4 5
0.8 0.65 40.7 1.68 14
1.2 0.14 7.2 0.24 13
9.4 0.56 1.4 0.16 8
- 0.11 1.2 0.31 4 - 114 5.4 104
7.6 2.2 36 1.3 4.7
17 0.57 1.1 0.06 8.5
4 - 114 5.4 104
7.6 2.2 36 1.3 4.7
17 0.57 1.1 0.06 8.5
0.3 - 3.7 0.7 24
38 4.7 207 10 120
5.5 - - 6.9 7.7
6
22
17
14
0.5
129
1.3
33
129
1.3
33
30
180
7.0
7
8
241
400
7200 1350
83,600 10,500
4070 380
251
28
16,400 185
140,000 19,000
251
28
16,400 185
140,000 19,000
48
3
254,000 35,000
7.4
-
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9
144
55
~27
~2
622
60
53
622
60
53
22
670
-
10
6.5
1.1
~37
~3
77
15
17
77
15
17
103
222
6.7
11
3.11
0.7
3.03
1.09
20
1.0
0.5
20
1.0
0.5
16.4
36
6.2
12
4540
160
2740
32.1
55
1
12,600
55
1
12,600
8.5
20,338
6.5
202
Key to Values- Groundwater:
(1) Rainwater from Menlo Park, California;
(2) Average rainwater from sites in North Carolina and Virginia;
(3) Composition of the Rhine River as it leaves the Alps;
(4) Stream draining igneous rocks in the Washington Cascades;
(5) Jump-Off Joe Creek, southwestern Oregon, wet season, November,
1990;
(6) Jump-Off Joe Creek, southwestern Oregon, dry season, September,
1991;
(7) Great Salt Lake, Utah;
8) Average seawater;
(9) Groundwater from limestone of the Supai Formation, Grand Canyon;
(10) Groundwater from volcanic rocks, New Mexico;
(11) Groundwater from a spring, Sierra Nevada Mountains: short residence
time;
(12) Groundwater from metamorphic rocks in Canada: long residence time.
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Conti.. surface & ground water

When water seeps below the surface, it passes
through the soil where microbial respiration
processes release CO2. As water encounters the
CO2, the pH is lowered, and the water can
dissolve more minerals.

At higher temperatures, minerals dissolve more
readily. Deep groundwater tends to be warmer
(e.g, the source of water from hot springs) thus
higher mineral content.
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Factors controlling groundwater composition:
here
(1) geologic materials groundwater
(2) type of reactions taking place, and
(3) contact time, or length of time groundwater
has been in contact with the rocks. The contact
time may vary from a few days to more than
10,000 years.
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Origin of Saline Groundwater




Typically, groundwater has a total dissolved solids
(TDS) content of less than 250 milligrams/liter
(mg/L).
Groundwater with a TDS > 100,000 mg/L is found
in some cases.
Sea water has a TDS content of approximately
35,000 mg/L)
Saline groundwater has been found in a variety of
geologic environments, commonly in marine
sedimentary rocks, but also in ancient metamorphic
and igneous rocks.
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Saline Groundwater
Saline groundwater can form in at least three ways:
(1) from trapped sea water;
(2) from dissolving highly soluble minerals;
(3) as a result of a long contact time with rocks, and
thus chemical reaction time with surrounding rocks.
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Examples of Groundwater conditions




Trapped Sea Water or pore (connate water). When marine
sediments are deposited, some sea water commonly
remains trapped between the mineral grains. Connate
water later may migrate through the rocks as groundwater.
Highly Soluble Minerals. Groundwater encountering
easily dissolved minerals such as gypsum (CaSO4.2H2O)
or halite (NaCl), will become saltier.
Rock water: Contact Time. Groundwater that follows deep
paths below the ground may be in contact and able to react
with rocks for thousands or tens of thousands of years.
This groundwater will acquire a higher TDS with time.
Sea spray, carried aloft by winds blowing across the
ocean, contributes to dissolved constituents in rainwater.
Sea spray is the primary source of chloride (Cl−) in
rainwater and a significant amount of sodium (Na+).
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WASTEWATER TREATMENT (L22-24)
Once
water has been used it becomes wastewater.
Wastewater is recovered from domestic or industrial sources.
If the water is to be returned back to the natural environment,
then it has to meet certain requirements.
Generally wastewater should not contain UNACCEPTABLE
levels of toxic chemicals or organisms.
Typical properties of untreated sewage water include: BOD
(250mg/L); COD (500mg/L); total solids (720mg/L),
suspended solids (220 mg/L); total phosphorous (8mg/L); total
nitrogen (40mg/L); pH (6.8); other components depending on
whether it is domestic wastewater or industrial wastewater.
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The guidelines for water
The guidelines for water to be used for irrigation
are different from those for drinking water. In order
to meet the guidelines, a variety of treatment
procedures have been developed.
 Treatment may include physical, chemical and
biological processes operating sequentially or
simultaneously.
 Example of specific requirement include: BOD
(15mg/L), SS (15mg/L) and Total phosphorous
(1 mg/L); etc.

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210